1. Field of the Invention
The present invention relates to a method for predicting the quantity of pictures that can be taken. In particular, this invention relates to a method that is applied to a digital still camera and utilizes the residual power of the battery to predict the quantity of pictures that can be taken.
2. Description of the Related Art
Recently, because the technology of digital still cameras has rapidly developed, digital still cameras have become popular and the capacity and speed of the memory cards used in the digital still cameras has also greatly improved. Moreover, the power supply, such as batteries, has also improved.
Reference is made to FIG. 1, which shows a schematic diagram of a status display in a digital still camera of the prior art. The digital still camera usually displays the capacity status of the memory card and the power status of the battery via a memory FIG. 11a and a battery FIG. 12a. In generally, the capacity of the memory card is displayed by a memory FIG. 11a, and the digital still camera 10a predicts and displays the available quantity of pictures that can be taken by calculating the residual capacity of the memory card according to the capacity or the number of pixels required for a single picture as set by the user. For displaying the residual power of the battery, the hardware of the digital still camera 10a includes a plurality of voltage detectors with different voltage levels to detect the power of the battery and display the residual power of the battery according to the detecting result from the voltage detectors. Furthermore, some digital still cameras 10a calculate the power required for different operational functions 13a, such as a picture-taking function or a picturing-viewing function, to predict and display the available time when the user switches to a specific operational function 13a. 
Because lithium batteries are light and thin, and can be recharged, lithium batteries are popularly designed to match the digital still camera. However, in order to match the digital still camera, the dimensions of the lithium batteries for different digital still cameras are different. Also, lithium batteries cannot be exchanged making them inconvenient for users.
Furthermore, because the digital still camera respectively displays the related information by detecting the status of the memory card or the battery, the user cannot exactly know how many pictures can be taken by the user based upon the residual power of the battery. If the user is informed to replace the battery by the detecting method of the prior art, the suggestion is always issued when the residual power of the battery is too low. At this moment, the user cannot take any more pictures and may lose an opportunity to take an important picture.